For the preparation of 1,3-bis(3-aminopropyl)-tetramethyldisiloxane, a method involving hydrosilylation reaction of an allylamine having an amino group protected with tetramethyldisiloxane, followed by deblocking of the protective group is known in the art. For example, use of trimethylsilylallylamine as the allylamine having an amino group protected is reported in J. Org. Chem, Vol. 24, page 119, 1959, and use of N-benzylideneallylamine is disclosed in JP-B 55953/1995.
These methods, however, have the problem that a substantial amount of an isomer in which internal addition has occurred rather than terminal addition forms during hydrosilylation reaction. As a result, 1-(2-aminopropyl)-3-(3-aminopropyl)tetramethyldisiloxane is admixed in the end compound. This isomer is less heat stable than the end compound, 1,3-bis(3-aminopropyl)tetramethyldisiloxane. When 1,3-bis(3-aminopropyl)tetramethyldisiloxane containing the isomer is used in the polyimide-modifying application where heat resistance is required, the performance is below the desired level.
Also, the step of deblocking the protective group from the reaction product resulting from hydrosilylation reaction tends to allow formation of by-products. In one example wherein the protective group is a trimethylsilyl group, equilibration reaction can occur when desilylation is carried out by adding water or alcohol, whereby (3-aminopropyl)pentamethyldisiloxane forms as a by-product, resulting in a reduced yield.
This problem can be avoided to some extent by a process including once deblocking the protective group with an acid, separating the resulting salt, and reacting with alkali. This process requires a very cumbersome operation.
Another known method for preparing 1,3-bis(3-aminopropyl)tetramethyldisiloxane is by subjecting an allylamine and a dimethylalkoxysilane to hydrosilylation reaction in the presence of a platinum complex catalyst having an olefin, a derivative thereof or a siloxane derivative thereof as the ligand and hydrolyzing the resulting product (see JP-A 304094/1990). Like the above method, this method also gives rise to the problem that a substantial amount of an isomer in which internal addition has occurred rather than terminal addition forms during hydrosilylation reaction, and as a result, 1-(2-aminopropyl)-3-(3-aminopropyl)tetramethyldisiloxane is admixed in the end compound. Moreover, since the catalyst used is special, it is not readily available and expensive.
There is a need to have a method for preparing 1,3-bis(3-aminopropyl)tetramethyldisiloxane of quality in a commercially advantageous manner.